The effects of gas flow rate, reaction temperature, particle size, and time on thermal decomposition of pyrite have been investigated between 673 and 1073 K in a nitrogen gas environment in which the gas-solid contact is effective. The decomposition reaction is well represented by the "shrinking core" model and can be divided into two regions with different rate controlling step. The rate-controlling step was found to be the heat transfer through the gas film for low conversion, but the mass transfer through product ash layer for high conversion. The activation energies for the heat transfer through the gas film and mass transfer through product ash layer-controlled cases were calculated as 113 and 96 kJ mol(-1), respectively. (C) 2003 Elsevier B.V. All rights reserved.